Éric Sansault’s scientific contributions

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Publications (5)


Citizen Data Speak on the Diversity of Odonata in Ponds Surrounded by Crop Fields
  • Article
  • Full-text available

December 2024

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7 Reads

The Bulletin of the Ecological Society of America

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Justine Léauté

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Éric Sansault

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Download

The study area. (a) An example of a digital map of the area surrounding a water body. Circles represent the four spatial scales of 200‐, 400‐, 800‐, and 1600‐m radii at which the effect of landscape composition on species richness was quantified. Study sites are represented in blue, intensive agriculture in yellow, forested areas in green, and urban areas in light gray. White background refers to any other land types, such as extensive agriculture, vineyard, or grassland. Lines represent streams and rivers. (b) The distribution of the 729 water bodies within this area. (c) Its localization, Indre‐et‐Loire (France).
Scale‐dependent effects of the proportion of intensive agriculture on the species richness. We report the drop in residual deviance (percentage) of the negative binomial regressions between overall (top raw) and autochthonous (bottom raw) species richness and the proportion of intensive agriculture and at four spatial scales for all Odonate species (circles), dragonflies (diamonds), and damselflies (triangles). Each model was applied to the full dataset without any restriction (759 water bodies), to a moderately constrained dataset that excluded all water bodies that were sampled only once (225 water bodies), and to a highly constrained dataset that only considered the water bodies that were visited during all three phenological periods (45 water bodies).
The effect of intensive agriculture on species richness. Average (+SD) standardized partial regression coefficients (***p < 0.001, **p < 0.01, *p < 0.05) from generalized linear mixed model averaging on the proportion of intensive agriculture for both all (a) and autochthonous species (b) and by discriminating damselflies (Zygoptera, white bars) and dragonflies (Anisoptera, black bars). The models were run at the landscape scales that best predict species richness when using the full dataset (see Figure 2). Each model was applied to the full dataset without any restriction (759 water bodies), to a moderately constrained dataset that excluded all water bodies that were sampled only once (225 water bodies), and to a highly constrained dataset that only considered the water bodies that were visited during all three phenological periods (45 water bodies). The scale differs between overall (a) and autochthonous (b) species.
Ranking of autochthonous damselflies (a) and dragonflies (b) from (top to bottom) the least to the most tolerant to the presence of surrounding intensive agricultural landscapes. For each species, the boxplot represents the distribution of the sites where the species reproduce according to the percentage of intensive agriculture measured within the 1600‐m buffer area. Each species is ranked according to the median percentage of intensive agriculture at which they were observed. The red dashed line corresponds to the median value of the 729 sampled sites. Only autochthonous species observed on five or more sites were included (n = number of ponds for each species).
Detecting the effect of intensive agriculture on Odonata diversity using citizen science data

December 2024

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170 Reads

Agricultural areas represent one of the major ecosystems of the world. Intensification of agricultural practices produced openfields characterized by low biological diversity. Nevertheless, the distance up to which intensive agricultural fields alter surrounding natural systems is rarely quantified. We determined the spatial scale at which agricultural landscapes alter the diversity of Odonates, a key taxon in wetland ponds, and we tested to what extent citizen science data can be used reliably for this purpose. We compiled 7731 observations made in a portion of the region Centre‐Val‐de‐Loire (France) over 10 years by naturalists on 729 water bodies to analyze the effect of agricultural landscapes (mainly wheat, rapeseed, sunflower) on the species richness of both damselflies and dragonflies in lentic systems. Sixty species were reported over the 10‐year period. For dragonflies, intensive agricultural landscapes best explained their richness at the scales of 800 and 1600 m for overall and autochthonous species, respectively, when using the full dataset. The spatial scale was smaller for damselflies, at 200 m for both overall and autochthonous species. These distances were not severely impacted when constraining the data to consider several biases. Multimodel averaging showed that the proportion of intensive agriculture decreased species richness, despite the potential biases inherent to an imperfect database acquired by citizens. This imperfect citizen dataset allows to infer the lowest effect size of agriculture on species richness. Quantitatively, this effect was more important for autochthonous species. Interestingly, both relatively rare taxa and common or generalist species can be under threat in intensive agricultural landscapes, calling for more ecotoxicological studies. The influence of agricultural practices from a distance implies that conservation and management plans of wetland ponds should consider the landscape ecological characteristics and not only the pond features. Conservation efforts focusing too locally on a site may be undermined because intensive agriculture from a distance limits the potential for the site to recover highly diverse communities. These distant effects should be integrated by policy‐makers when deciding which wetland pond should benefit from a conservation plan or which conservation action may be planned, implementing, for instance, buffer zones and/or ecological corridors composed of natural vegetation.


Figure 1. Leucorrhinia albifrons ♂ surveillant son territoire ; on constate la large présence des herbiers à Characées par transparence en arrière-plan (© É. Sansault). Leucorrhinia albifrons ♂ surveying its territory, where Characeae are abundant aquatic plants.
Figure 2. Habitat de Leucorrhinia albifrons, L. caudalis et L. pectoralis dans le parc de Rigny-Ussé : étang oligotrophe présentant des massifs de Nymphaea alba (premier plan), des herbiers à Characées (second plan) et situé dans un boisement de feuillus (arrière-plan) (© É. Sansault). Natural habitat of L. albifrons, L. caudalis and L. pectoralis in the Rigny-Ussé park: an oligotrophic pond with Nymphaea alba and Characeae, within a hardwood forest. Évaluation de l'état de conservation de la station L'observation de 10 mâles territorialisés lors de deux comptages rapprochés et la récolte de 23 exuvies lors d'un seul passage sur 50 m de berge (soit 0,46 exuvie par mètre linéaire de recherche) indiquent une population en « bon » état de conservation (DUPONT, 2010 : 144). Ces effectifs restent toutefois un minimum et ne correspondent pas à une estimation de la taille de la population par capture-marquage-recapture ou par récolte d'exuvies. Précisons également que la récolte d'exuvies n'a été effectuée que sur environ 23 % du linéaire total de berge favorable et qu'il est par conséquent possible d'extrapoler ce nombre d'exuvies à une centaine présentes ce même jour. Ces éléments permettent d'estimer les effectifs entre « bons » et « excellents ». Les éléments caractérisant le site d'étude (cf Matériel & méthodes) permettent de considérer la qualité de l'habitat comme « excellente ». Par ailleurs, les facteurs externes de dégradation semblent assez peu nombreux. En effet, compte tenu de la structure paysagère principalement forestière et de la gestion sylvicole locale extensive, l'impact anthropique sur la zone riveraine est jugé comme « faible » sinon « nul ». Concernant les facteurs de dégradation internes au plan d'eau, signalons la présence en forte densité de Perches soleil Lepomis gibbosus (Linnaeus, 1758), de quelques Brochets Esox lucius Linnaeus, 1758 mais la très faible abondance (sinon l'absence) de poissons benthivores ayant un fort impact négatif sur la végétation aquatique et les habitats larvaires. De plus, aucune activité récréative n'est signalée sur cet étang (chasse, pêche, navigation…). L'état de conservation du site est par conséquent jugé comme « excellent ».
Figure 3. Leucorrhinia albifrons : (a) ♂ sur son perchoir et accouplement (b) (© É. Sansault). Leucorrhinia albifrons: perched ♂ (a) and mating (b).
Découverte de Leucorrhinia albifrons en région Centre-Val de Loire et structure des populations du centre-ouest de la France (Odonata : Libellulidae)

December 2019

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244 Reads

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1 Citation

In France, Leucorrhinia albifrons is a rare species with a fragmented distribution and three areas of occupancy: in the Nouvelle-Aquitaine, in the Bourgogne-Franche-Comté and in the Pays de la Loire regions. Close to this last region, the discovery of a population in Indre-et-Loire department in June 2017 represents the first record of the species for the Centre - Val de Loire region. The conservation status of this population seems favorable regarding population size and habitat quality. Although it is still unknown wheter this population remains from an ancient bigger population or follows a recent colonization, it seems to be isolated from the other sites found in the central western part of France. Oncoming monitoring should provide new information about the population's origins.


Distribution of the various types of habitats within the 1 km radius study site (a) and zoom of the detection zone (red polygon) around the pond, which comprised all the detections (b). The white dots indicate the individuals that were not identified (11 detections) and each colored dot shows the position of the identified individuals (five identified individuals; one has two points on the map). The crosses show the position of the dead individuals (N = 6). The black star indicates the location where individuals were released. No tagged individual was detected outside this maturation zone within the study site. (Color figure online)
Illustration of two immature individuals equipped with the diode system. Individuals were marked on the wings to identify them when they were detected. Photographs: Eric Sansault
Path of the transects used to detect tagged L. caudalis individuals during the study period. The shaded area around transects indicates the maximal detection distance (118 m) on each side of each transect
Proportions (%) of habitat in the detection zone and proportions of individuals detected by the RECCO® system in these different habitats
Telemetry reveals the habitat selected by immature dragonflies: implications for conservation of the threatened dragonfly Leucorrhinia caudalis (Odonata: Anisoptera)

February 2019

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538 Reads

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9 Citations

Journal of Insect Conservation

Aurélia LeNaour

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Eric Sansault

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[...]

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Determining how species use different habitats during critical phases of their development is one of the crucial challenges that conservation biology meets. However, habitat requirements remain unknown for most species, in particular for the rarest and most threatened which by definition are difficult to study. Here, we used animal-borne telemetry to identify the habitat of the sexually immature adults in the threatened dragonfly Leucorrhinia caudalis. We used an harmonic radar with customized tags fixed on the back of the abdomen of flying immature dragonflies to monitor their position within an area composed of various types of habitats including open areas, forest and water bodies. From 62 tagged individuals, we obtained 23 detections, all within a quite restricted area around the pond of emergence. About 75% of the detections happened in the forest canopy and the individuals were likely positioned at the top of the trees. The relatively low detection rate was probably due to high predation within the study area during the maturation phase in this dragonfly but long-range dispersal cannot be excluded. The use of forest canopy as a maturation habitat is an important knowledge for planning conservation strategies in this endangered species, especially for populations living in areas without any protection status. Although technological constraints are still limiting its efficiency, animal-borne telemetry appears to be useful to determine precisely habitat selection by rare species.


Figure 2. Nombre total de données par maille 5 x 5 km disponibles dans la base de données INVODCILIF sur la période 1957-2009.
Figure 3. Évolution du nombre de données brutes relatives aux espèces PRA, en cumulatif (annuel) par département, depuis 1960.
Figure 4. Répartition des espèces PRA par maille de 5 x 5 km en région Centre.
Plan national d'actions en faveur des Odonates - déclinaison Centre - Val de Loire

December 2012

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137 Reads

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4 Citations

Conservation of Odonata species (dragonflies and damselflies) contributes to the maintenance of biodiversity and to the functioning of natural ecosystems. They are particularly sensitive to environmental changes as they are potentially exposed to threats in both aquatic and terrestrial medium. A national plan for the conservation of Odonata species was launch in 2010 in France, with the aim to assess the population level of 18 species that were declared under threat. This national plan is downscaled here at the level of the region Centre. This regional plan reviews our knowledge on population level of several Odonata species, and suggests action plans for the period 2013-2017 in terms of increasing knowledge, conservation management and communication at several levels. This approach aims at stabilizing these threaten species in the region Centre by networking all actors in the conservation of Odonata species. The review shows that the sampling effort has increased substantially since 2000s, although it remains heterogeneous over the region Centre territory. The region Centre hosts 8 species targeted by the national plan (priority 1). In addition, the regional plan targets 13 species of priority level 2 and 9 of priority level 3. The regional plan proposes 9 actions to increase our knowledge. As specified in the national plan, the species Leucorrhinia caudalis is among the main targets of this plan. The Loire Valley is also of concern as 2 species of priority level 1, Gomphus flavipes and Ophiogomphus cecilia, are associated to this particular freshwater system. Finally, 5 actions for conservation management / administration, and 3 actions for communication and training are proposed with the aim to protect these Odonata species and their habitats. --- La préservation des Odonates (libellules et demoiselles) contribue de façon importante au maintient de la biodiversité et au bon état de conservation des écosystèmes. Les Odonates sont confrontés aux menaces environnementales dans les deux milieux, aquatiques et terrestres. Un Plan National d’Actions (PNA) en faveur des Odonates a été lancé en France en 2010. Ce plan vise à évaluer l’état de conservation de 18 espèces d’Odonates jugées menacées sur le territoire métropolitain. Ce PNA est décliné ici en région Centre. Cette déclinaison intègre une synthèse des connaissances sur l’état des populations des espèces d’Odonates visées, et propose des actions pour la période 2013 2017 en termes d’approfondissement des connaissances, de gestion conservatoire et de sensibilisation à plusieurs niveaux. Cette démarche vise à permettre, en associant les acteurs engagés dans la conservation des Odonates, le maintient en région Centre de ces espèces menacées. La synthèse générale montre que l’effort de prospection s’est intensifié depuis le début des années 2000. Cependant, cet effort est encore hétérogène sur le territoire de la région Centre. La région Centre est occupée par 8 espèces du PNA (espèces de priorité 1). Le Plan Régional d’Actions en faveur des Odonates (PRAO) incorpore également 13 espèces dites de priorité 2 et enfin 9 espèces de priorité 3. Le PRAO Centre développe 9 actions d’approfondissement des connaissances. Comme demandé dans le PNA, la Leucorrhine à large queue (Leucorrhinia caudalis) est une des cibles principales de ce plan d’actions. Le fleuve Loire constitue aussi un enjeu national pour au moins 2 espèces, le Gomphe à pattes jaunes (Gomphus flavipes) et le Gomphe serpentin (Ophiogomphus cecilia), qui sont fortement associées aux habitats particuliers à ce système fluvial. Enfin, cinq actions de gestion conservatoire / administration et 3 actions de formation et sensibilisation sont proposées dans le but général d’assurer la protection de ces espèces Odonates et de leurs habitats.

Citations (3)


... En Europe, les données réunies depuis deux décennies illustrent les déplacements de L. albifrons et les modifications de son aire de répartition à l'échelle régionale. Elle a ainsi été observée pour la première fois en Belgique en 2016 (De Knijf & Berx 2019), de même que dans la Vallée de la Loire en 2017 (Sansault et al. 2019). En Hollande, elle a été revue en 2005, après plusieurs décennies d'absence (De Boer & Wasscher 2006). ...

Reference:

Situation actuelle de Leucorrhinia albifrons (Burmeister, 1839) en Suisse (Odonata: Libellulidae)
Découverte de Leucorrhinia albifrons en région Centre-Val de Loire et structure des populations du centre-ouest de la France (Odonata : Libellulidae)

... Several animal species require distinct habitats for larval development, maturation, overwintering, foraging, and/or oviposition and depend on both aquatic and terrestrial habitats (e.g., Le Naour et al., 2019;Pope et al., 2000;Wiens, 1989). For these species, agricultural practices can directly influence the habitats used during both their terrestrial and aquatic life periods, thereby altering the services that these species can provide (Priyadarshana & Slade, 2023;Raitif et al., 2019). ...

Telemetry reveals the habitat selected by immature dragonflies: implications for conservation of the threatened dragonfly Leucorrhinia caudalis (Odonata: Anisoptera)

Journal of Insect Conservation

... However, riverine habitats and species have been poorly investigated by volunteers and these protocols have been designed to survey spatial and temporal trends in adults on a large scale but are not suitable for local riverine species surveys. Riverine species are also often neglected on the Natura 2000 sites where they are present (Costes et al., 2017) and the French action plan in favour of dragonflies identifies a need for quantitative data and calls for the development of effective standardised protocols (Dupont, 2010). ...

Plan national d'actions en faveur des Odonates - déclinaison Centre - Val de Loire